So-called "safety" papers, which can be used in particular for manufacturing handwritten payment documents and official documents such as checks, travelers' checks, etc., must be protected from any attempts to falsify the writing or stamps carried on the papers, using any kind of chemical reagent or modern process, such as an ink-erasing pencil. The colored inks currently employed for writing by hand or printing by means of inking pads can be cleanly removed using these erasing pencils.
However, the majority of safety papers currently available on the market react inadequately to such attempts at falsification with ink-erasing pencils. This often causes the appearance of a fluorescent yellow color which is not easily visible to the naked eye and which furthermore cna prove troublesome for certain uses.
Thus, French Pat. No. 2,365,656 describes a safety paper containing a chemical sensitizing composition based on an acid-base indicator which is very sensitive to pH variations. The indicator is selected especially from the group comprising the phthaleins or sulfophthaleins. When the pH rises (due to the action of the erasing pencil), the paper develops a coloration. However, all the products described therein are difficult to use in paper manufacture, mainly because of the conditions governing their solubilization, use pH, reversibility or stability.
French Pat. No. 2,399,505, and its Certificate of Addition No. 2,402,739 describe a safety paper containing a chemical sensitizing composition based on an oxypyrenetricarboxylic acid salt called Pyranine. The action of an erasing pencil on such papers develops a fluorescent yellow coloration.
French Pat. No. 2,406,027, and French Pat. No. 2,427,436, as well as its Certificate of Addition No. 2,432,576, describe a safety paper containing dinitrophenols which turn a non-fluorescent yellow under the action of an erasing pencil.
Finally, French Pat. No. 2,410,702 describes a safety paper containing a chemical sensitizing composition composed of Pyranine in association with an optical brightener along with a variety of other compounds. The action of an erasing felt pen on a paper of this kind produces a fluorescent yellow coloration.
The object of this invention is to propose a compound which, when associated with a paper, renders it unfalsifiable even by erasing pencils, by instantaneously developing a coloration which can be clearly detected by the naked eye.